We investigate differences in Spitzer/IRAC 3.6 and 4.5 μm photometry that depend on observing strategy. Using archival calibration data, we perform an in-depth examination of the measured flux densities (fluxes) of 10 calibration stars, observed with all the possible observing strategies. We then quantify differences in the measured fluxes as a function of (1) array mode (full or subarray), (2) exposure time, and (3) dithering versus staring observations. We find that the median fluxes measured for sources observed using the full array are 1.6% and 1% lower than those observed with the subarray at [3.6] and [4.5], respectively. In addition, we found a dependence on the exposure time such that for [3.6] observations, the long frame times are measured to be lower than the short frame times by a median value of 3.4% in full array and 2.9% in subarray. For [4.5] observations, the longer frame times are 0.6% and 1.5% in full and subarray, respectively. These very small variations will likely only affect science users who require high-precision photometry from multiple different observing modes. We find no statistically significant difference for fluxes obtained with dithered and staring modes. When considering all stars in the sample, the fractional well depth of the pixel is correlated with the different observed fluxes. We speculate the cause to be a small nonlinearity in the pixels at the lowest well depths where deviations from linearity were previously assumed to be negligible.

中文翻译：

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暖斯皮策 IRAC 光度测量：依赖于观察模式和曝光时间

我们调查了 Spitzer/IRAC 3.6 和 4.5 μm 光度测量的差异，这取决于观察策略。使用存档校准数据，我们对 10 颗校准星的测量通量密度（通量）进行了深入检查，并使用所有可能的观测策略进行了观测。然后，我们将测量通量的差异量化为 (1) 阵列模式（全阵列或子阵列）、(2) 曝光时间和 (3) 抖动与凝视观察的函数。我们发现，使用全阵列观察到的源测量的中值通量分别比使用 [3.6] 和 [4.5] 的子阵列观察到的低 1.6% 和 1%。此外，我们发现了对曝光时间的依赖性，因此对于 [3.6] 观察，长帧时间被测量为低于短帧时间，全阵列中值为 3.4%，子阵列中为 2.9%。对于 [4.5] 观察，较长的帧时间分别为全阵列和子阵列的 0.6% 和 1.5%。这些非常小的变化可能只会影响需要从多种不同观察模式进行高精度光度测量的科学用户。我们发现使用抖动和凝视模式获得的通量没有统计上的显着差异。当考虑样本中的所有恒星时，像素的分数井深度与不同的观测通量相关。我们推测原因是最低井深度的像素中存在小的非线性，之前假设与线性的偏差可以忽略不计。这些非常小的变化可能只会影响需要从多种不同观察模式进行高精度光度测量的科学用户。我们发现使用抖动和凝视模式获得的通量没有统计上的显着差异。当考虑样本中的所有恒星时，像素的分数井深度与不同的观测通量相关。我们推测原因是最低井深度的像素中存在小的非线性，之前假设与线性的偏差可以忽略不计。这些非常小的变化可能只会影响需要从多种不同观察模式进行高精度光度测量的科学用户。我们发现使用抖动和凝视模式获得的通量没有统计上的显着差异。当考虑样本中的所有恒星时，像素的分数井深度与不同的观测通量相关。我们推测原因是最低井深的像素中的小非线性，其中线性偏差以前被认为可以忽略不计。